Effective clinical practice of any kind requires reliable diagnosis and risk-cost-benefit management for the short, medium and long-term, which is evidence-based. This is the case for clinical nutrition as well. Clinical nutrition rarely stands alone, but is integral to most of primary to tertiary health care in all of its disciplines (adult internal medicine, pediatrics, obstetrics and gynecology, surgery and psychiatry) and systems (e.g. gut, CNS, reproductive, hematologic, musculoskeletal). In the past, the role of food intake in disease expression has been under-recognized, leading to failure of nutritional diagnosis, without which there will be no nutritional management. Important examples are in disorders of immune function, those which are neurobehavioral, and of reproduction. Advances in nutritional epidemiology, food chemistry (especially the physical properties of food, and its phytochemistry) and in nutritional assessment (especially in body composition and in molecular nutrition) are providing more scope for nutritional approaches to the changing patterns of infections, and to the so called chronic diseases and mental health, which contribute the major burden of disease world-wide. All clinicians require a basic understanding of food health relationships and their relevance in the field in which they practice.